The present invention relates to a mixture comprising
a) a polymer which contains at least one L=X structural unit,
b) a triplet emitter compound and
c) a carbazole compound or a soluble neutral molecule.
The invention is furthermore directed to organic electroluminescent devices which contain the mixture according to the invention.
The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. A development in the area of organic electroluminescent devices are phosphorescent OLEDs. These have significant advantages owing to the higher achievable efficiency compared with fluorescent OLEDs.
However, there is still a need for improvement in the case of phosphorescent OLEDs. This applies, in particular, to the efficiency and lifetime of the devices.
In accordance with the prior art, electron-conducting materials, inter alia ketones (for example in accordance with WO 04/093207) or triazine derivatives (for example in accordance with DE 102008036982), are used as matrix materials for phosphorescent emitters. In particular with ketones, low operating voltages and long lifetimes are achieved, which makes this class of compound a very interesting matrix material. However, there is still a need for improvement in the case of the use of these matrix materials, as in the case of other matrix materials, in particular with respect to the efficiency and lifetime of the devices.
The prior art furthermore discloses organic electroluminescent devices which contain a phosphorescent emitter doped into a mixture of two matrix materials.
US 2007/0252516 discloses phosphorescent organic electroluminescent devices which contain a mixture of a hole-conducting matrix material and an electron-conducting matrix material. Improved efficiency is disclosed for these OLEDs. An influence on the lifetime is not evident.
US 2007/0099026 discloses white-emitting organic electroluminescent devices in which the green- or red-emitting layer comprises a phosphorescent emitter and a mixture of a hole-conducting matrix material and an electron-conducting matrix material. The hole-conducting materials disclosed are, inter alia, triarylamine and carbazole derivatives. The electron-conducting materials disclosed are, inter alia, aluminium and zinc compounds, oxadiazole compounds and triazine or triazole compounds. Further improvements are also still desirable for these OLEDs.
WO 2008/086851 A1 discloses carbazole compounds and the use thereof in organic electroluminescent devices, in particular as matrix material in phosphorescent devices, in which ketone compounds may likewise be present.
WO 2005/040302 A1 discloses organic semiconductors comprising a polymer, compounds containing L=X structural units and triplet emitter compounds. The compounds mentioned therein have good solubility and are readily accessible synthetically.
Nevertheless, there continues to be a need for improvement with respect to solubility for solution-processable systems and with respect to lifetime and efficiency.
The technical object on which the invention is based was therefore the provision of a mixture which can be processed simply from solution and, in an organic electroluminescent device, results in a very long lifetime and good efficiency.
The object is achieved in accordance with the invention by a mixture comprising
a) a polymer which contains at least one L=X structural unit,
b) a triplet emitter compound and
c) a carbazole compound or a soluble neutral molecule,
where the following applies to the symbols and indices used:
    L is on each occurrence, identically or differently, C(R1)2, PR1, AsR1, SbR1, BiR1, P(R1)3, As(R1)3, Sb(R1)3, Bi(R1)3, S(R1)2, Se(R1)2, Te(R1)2, (R1)2S(═O), (R1)2Se(═O) or (R1)2Te(=0);    X is on each occurrence, identically or differently, O, S, Se or NR2;    R1 is on each occurrence, identically or differently, H, D, F, CN, N(R2)2, a straight-chain, branched or cyclic alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms, which may be substituted by R3 or also unsubstituted, where one or more non-adjacent CH2 groups may be replaced by —R4C═CR4—, —C═C—, Si(R4)2, Ge(R4)2, Sn(R4)2, C═O, C═S, C═Se, C═NR4, —O—, —S—, —NR4 or —CONR4— and where one or more H atoms may be replaced by F, Cl, Br, I, CN or NO2, or an aromatic or heteroaromatic ring system having 1 to 60 C atoms, which may be substituted by one or more radicals R3, where two or more substituents R1, together with the atoms to which they are bonded, may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another; where at least one group R1 has a bond to a further structural unit of the polymer;    R2 is on each occurrence, identically or differently, a straight-chain, branched or cyclic alkyl or alkoxy group having 1 to 22 C atoms, in which, in addition, one or more non-adjacent C atoms may be replaced by —R4C═CR4—, —C≡C—, Si(R4)2, Ge(R4)2, Sn(R4)2, —NR4—, —O—, —S—, —CO—O—, —O—CO—O—, where, in addition, one or more H atoms may be replaced by fluorine, an aryl, heteroaryl or aryloxy group having 1 to 40 C atoms, which may also be substituted by one or more radicals R3, or OH or N(R3)2;    R3 is on each occurrence, identically or differently, R4 or CN, B(R4)2 or Si(R4)3; and    R4 is on each occurrence, identically or differently, H, D or an aliphatic or aromatic hydrocarbon radical having 1 to 20 C atoms.